When I stand far away and point a TV remote at it and push a button, the LED lights up; hence it appears to be working. However if I get within 1m of the sensor i.e. just stand in front of it without the remote, the LED flickers continually - almost as if a signal is bouncing off of me.

The sensor that I am using is not a TS0p1738 but rather the following: ZD1952

I therefore have two questions:
1) Why does the LED shine when I stand near the sensor but if I am further away only when pressing the remote.
2) Do I need to make same changes to accommodate the fact that the receiver is a ZD1952?